The present invention relates to a device for clamping and/or holding workpieces on a machine tool, e.g. on the work table of a grinder, and is embodied as a steady rest with three holding members that act on the workpiece to be held and that are disposed in the same plane and in a clampable housing and that can be actuated by a piston that is acted on by a pressure medium, of which members the two outer holding members are designed as mirror-image pivotable angle levers and can be adjusted in a controlled manner by means of control cams that cooperate with the free ends of the two outer holding members.
A steady rest of this type is known from DE 35 43 806 C2. For enlarging the insertion opening, in this design an additional adjusting movement of the center holding member can cause at least one of the two outer holding members to move beyond the clamping range of the steady rest. This is brought about in that the holding member has an articulated connection via a lever to the center holding member and the center holding member has a recess into which the end of the outer holding member can be introduced.
This steady rest has proved itself in practice in terms of holding workpieces on a lathe; however, it is not possible to use it with processing machines that have a flat bed, e.g., a grinder, because the holding members of the steady rest cannot be swivelled out of the loading region. For this to be possible, it would be necessary for the steady rest to move using a special slide. This would itself entail an additional work step and substantial complexity in terms of the construction. In addition, the repeatability accuracy would not be sufficient due to the change in the steady rest""s position.
It is therefore an object of the invention to provide a device for clamping and/or for holding workpieces on a machine tool of the type specified in the foregoing such that the device does not impede the process of loading the machine tool. On the contrary, it should be possible to move the holding members of the steady rest such that the loading region of the machine tool is completely clear so that there is even no problem clamping workpieces that have a pivot circle, e.g. a crankshaft, in the machine tool. In addition, it should not be necessary to change the position of the steady rest; rather, the housing of the steady rest should always maintain the position it has assumed so that there is a high degree of repeat clamping accuracy. The construction should not be very complex, but the device should also have high operational reliability, be easy to use, and offer great clamping accuracy.
This objective is inventively achieved by a device for clamping and/or for holding workpieces on a machine tool of the type cited in the foregoing in that the three holding members are supported in a separate intermediate member that is connected directly or via interposed elements to the piston that is actuated by a pressure medium and by means of which the intermediate member can be displaced in the housing in the direction of the workpiece, and in that the control cams, by means of which the outer holding members can be pivoted by the adjusting movements of the intermediate member, are formed in the walls of the housing that run laterally adjacent to the two outer holding members.
It is useful to embody the center holding member as a roller rotatably borne in the intermediate member, with the end of the roller that faces the workpiece projecting, as a cylinder, or as a stationary slide element, whereby the axial length of a receiving space of the housing associated with the intermediate member is approximately the same as the length of the intermediate member and the parts of the outer holding members projecting therefrom.
It is also useful for the intermediate member to comprise two plates that can be clamped together so that it is easy to install the intermediate member and the holding members that are to be inserted therein.
The control cams inserted in the walls of the housing should each constitute a rectilinearly running in-feed region and an adjusting region associated with the pivot movements of the outer holding members, in which regions the outer holding members are guided by means of rollers borne on pins inserted therein. In order to avoid jams, the intermediate member should be provided with through-holes in the area of the pins that extend at least over the projected height of the control cams.
Furthermore expedient is affixing the piston, which acts on the intermediate member and which is actuated by pressure medium, preferably on both sides, directly to the intermediate member by means of a piston rod and inserting it in a cylinder that is securely connected to the housing. The receiving space of the housing and/or the interior of the intermediate member can also be acted upon by sealing air.
It is furthermore advantageous in terms of assembling the clamping device to provide the housing, on one of the longitudinal sides running parallel to the adjusting device of the intermediate member, with a projecting element by means of which the housing can be rigidly fixed directly or via an adapter to the tool table of the machine tool.
If a device for clamping and/or holding workpieces on a machine tool is embodied in accordance with the invention, it is very simple to completely remove the holding members of the steady rest from the loading region of a machine tool so that workpieces can be clamped unimpeded, especially on machine tools with a flat bed. The position of the housing of the clamping device is not changed; on the contrary, the holding members can be introduced into the housing by means of a servo-device that acts on the intermediate member carrying them, which servo-device is also used for feeding the outer holding members. Additional actuators are thus not required, nor does the installed position of the steady rest change, so that there is always a high degree of repeatable clamping accuracy.
The complexity of construction required for this is low if the control cams by means of which the outer holding members are actuatable are formed directly in the walls of the housing and are thus arranged stationary therein. Not only does this provide high clamping accuracy, but also available components are used, in this case the two side walls of the housing, so that the result is small structural width of the steady rest embodied as suggested. And since only a few components are necessary for holding the workpiece to be clamped, there is a high degree of operational reliability, the device is easy to use, and it has low susceptibility to interruptions.